UDO ISLAND, South Korea — On a cold, rainy morning, the sea women of this islet donned their black wetsuits, strapped on their goggles and swam out into the waves.

Over several hours, they dove to reach the sea bottom, holding their breath for about a minute before bobbing up to the surface. Sometimes, several dove in unison, their flippers jutting out together for a split second, looking like synchronized swimmers.

That illusion lasted until they resurfaced, one clutching an octopus, another a sea urchin, and until a closer look at the sunburned, leathery faces behind the goggles revealed women in their 50's, 60's and older.

The sea women here and on larger Cheju Island, off the southern coast of South Korea, are among the world's most skillful and toughest natural divers. Year round, they plumb the sea bottom with no scuba gear, in one- or two-minute dives that mix dexterity, desire and death.

"Every time I go in," said Yang Jung Sun, 75, "I feel as if I am going to the other side of the world. When I see something I could sell, I push myself in toward it.

"When I get out of breath, I push myself out of the water. It is all black in front of me. My lungs are throbbing. At that moment I feel I am dead. It happens every time. Every time. I tell myself I am not going to do that again. I always tell myself that. But greed makes me go back again."

Ms. Yang, above, earns about $30,000 a year.

Since the late 1970's, exports of sea products to Japan have made the sea women richer than they had ever imagined, allowing them to fix their houses, build new ones in Cheju City and send their daughters to college.

Some of the best divers, like Yang Hwa Soon, 67, not related to the older Ms. Yang, now make about $30,000 a year. Most dive 10 days each month but also work the fields. With tourism also popular here, many sea woman run restaurants and inns.

But their very success means that, within a decade or two, with the daughters choosing to work in the island's tourism industry or in the big cities, the 1,700-year history of Cheju's sea women will probably end. In 2003, 5,650 sea women were registered in Cheju, of whom 85 percent were over 50 years old. Only two were under 30.

Men dived until the 19th century but found the job unprofitable because they, unlike women, had to pay heavy taxes, said Ko Chang Hoon, a professor at Cheju National University. So the women took over what was considered the lowest of jobs and became the main breadwinners.

This clashed with Korea's Confucian culture, in which women have traditionally been treated as inferior, leading administrators from Seoul to bar the women from diving, ostensibly because they exposed bare skin while at sea. "The central government forbade the women from diving, but the women just gave them some abalone to look away," said Professor Ko, whose mother and grandmother were sea women.

Not surprisingly, the sea women's power was greatest in villages that relied more on sea products than on farming. On Mara Island, where sea products accounted for almost all sources of revenue until tourism became popular in recent years, sex roles were entirely reversed.

In a study of Mara Island, Seo Kyung Lim, a professor at Cheju National University whose mother was a sea woman, found that men took care of the children, shopping and feeding the pigs. Women ruled their households and their community.

If their husbands cheated on them, Professor Seo said, "they could simply tell them to get out of the house."

On Cheju, market forces prevailed over the Confucian preference for boys. "If people had a boy, they didn't celebrate," Professor Ko said. "If it was a girl, they celebrated, because they knew that the girl would dive and bring money to the family."

On Udo, though farming traditionally made up a third of revenues, with sea products accounting for the rest, women's status was also high. "We always made more money than the men," Yang Jung Sun said. "They just made enough to feed themselves. We paid for fuel and education. Everything."

Perhaps realizing that men, including the head of a local fishing association, sat within earshot, Ms. Yang added, with a smile that bridged the gap between her words and the reality: "How can women have more power at home? There's only one captain in a house and that's clearly the father."

The girls begin going to sea at age 8 or 10, first picking up seaweed near the shore. The best divers can plunge 40 feet deep and hold their breath for over two minutes. (To avoid overfishing, scuba gear remains illegal.)

With a flat tool attached to one wrist, the sea women try to dislodge abalone from under rocks. Occasionally, though, the abalone clamp down on the tool and trap one of them underwater. At least one sea woman dies every year while diving.

With the number of sea women declining, and with tourism giving Cheju men more opportunities, it is unclear what will happen to their daughters' status in their communities and home. What is clear, though, is the pervasive sense that the end of something is near.

"When I wanted to go deeper, until last year I would push myself to go deeper," Yang Hwa Soon said. "Now I feel I'm aging. When I want to go deeper, instead of pushing myself, I usually decide not to go. I started feeling older last year, after I turned 65."